title: Human infections with influenza A(H3N2) variant virus in the United States, 2011-2012.
abstract: BACKGROUND. During August 2011-April 2012, 13 human infections with influenza A(H3N2) variant (H3N2v) virus were identified in the United States; 8 occurred in the prior 2 years. This virus differs from previous variant influenza viruses in that it contains the matrix (M) gene from the Influenza A(H1N1)pdm09 pandemic influenza virus. METHODS. A case was defined as a person with laboratory-confirmed H3N2v virus infection. Cases and contacts were interviewed to determine exposure to swine and other animals and to assess potential person-to-person transmission. RESULTS. Median age of cases was 4 years, and 12 of 13 (92%) were children. Pig exposure was identified in 7 (54%) cases. Six of 7 cases with swine exposure (86%) touched pigs, and 1 (14%) was close to pigs without known direct contact. Six cases had no swine exposure, including 2 clusters of suspected person-to-person transmission. All cases had fever; 12 (92%) had respiratory symptoms, and 3 (23%) were hospitalized for influenza. All 13 cases recovered. CONCLUSIONS. H3N2v virus infections were identified at a high rate from August 2011 to April 2012, and cases without swine exposure were identified in influenza-like illness outbreaks, indicating that limited person-to-person transmission likely occurred. Variant influenza viruses rarely result in sustained person-to-person transmission; however, the potential for this H3N2v virus to transmit efficiently is of concern. With minimal preexisting immunity in children and the limited cross-protective effect from seasonal influenza vaccine, the majority of children are susceptible to infection with this novel influenza virus.
authors.affiliation: Influenza Division, National Center for Immunization and Respiratory Diseases, Centers for Disease Control and Prevention, 1600 Clifton Rd. NE, Atlanta, GA 30333, USA. sepperson@cdc.gov
authors.forename: Scott
authors.initials: S
authors.lastname: Epperson
authors.forename: Michael
authors.initials: M
authors.lastname: Jhung
authors.forename: Shawn
authors.initials: S
authors.lastname: Richards
authors.forename: Patricia
authors.initials: P
authors.lastname: Quinlisk
authors.forename: Lauren
authors.initials: L
authors.lastname: Ball
authors.forename: Mària
authors.initials: M
authors.lastname: Moll
authors.forename: Rachelle
authors.initials: R
authors.lastname: Boulton
authors.forename: Loretta
authors.initials: L
authors.lastname: Haddy
authors.forename: Matthew
authors.initials: M
authors.lastname: Biggerstaff
authors.forename: Lynnette
authors.initials: L
authors.lastname: Brammer
authors.forename: Susan
authors.initials: S
authors.lastname: Trock
authors.forename: Erin
authors.initials: E
authors.lastname: Burns
authors.forename: Thomas
authors.initials: T
authors.lastname: Gomez
authors.forename: Karen K
authors.initials: KK
authors.lastname: Wong
authors.forename: Jackie
authors.initials: J
authors.lastname: Katz
authors.forename: Stephen
authors.initials: S
authors.lastname: Lindstrom
authors.forename: Alexander
authors.initials: A
authors.lastname: Klimov
authors.forename: Joseph S
authors.initials: JS
authors.lastname: Bresee
authors.forename: Daniel B
authors.initials: DB
authors.lastname: Jernigan
authors.forename: Nancy
authors.initials: N
authors.lastname: Cox
authors.forename: Lyn
authors.initials: L
authors.lastname: Finelli
mesh_terms: D000293:Adolescent; D000328:Adult; D000818:Animals; D002648:Child; D002675:Child, Preschool; D004196:Disease Outbreaks; D005260:Female; D006801:Humans; D007223:Infant; D053118:Influenza A Virus, H1N1 Subtype / Q000235:genetics; D053122:Influenza A Virus, H3N2 Subtype / Q000235:genetics / Q000302:isolation & purification*; D007251:Influenza, Human / Q000453:epidemiology* / Q000635:transmission; D008297:Male; D008875:Middle Aged; D009976:Orthomyxoviridae Infections / Q000635:transmission / Q000662:veterinary; D013552:Swine; D013553:Swine Diseases / Q000635:transmission; D014481:United States / Q000453:epidemiology
keywords: influenza; public health; surveillance